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Being able to argue properly and rationally with other people is very important in life. If you know how to structure an argument correctly, and what fallacies to look out for, you will avoid being deceived or out-spoken by scams or faulty logic, and you will avoid making these mistakes yourself, which increases the credibility and force of your arguments.

The following are fallacies to look out for which are very common. But even more important than being able to spot fallacies is the following: always realise that you can be wrong. The strength of your convictions is irrelevant to their validity.

Also, it is important to recognise the difference between a valid argument and sound argument. Valid arguments are structurally correct in that no formal fallacy is committed, but this doesn’t make them true. A sound argument is one that is valid and deductively true. E.g.:

P1: Socrates is a man.

P2: All men die.

Conclusion: Therefore Socrates will die.

Circular Reasoning / Begging the Question

People use the expression “which begs the question” in everyday speech when that they really mean is “raises the question”. To beg the question is actually a logical fallacy whereby your premises entail the conclusion, and the premises are dubious and implicitly assume that conclusion.

I will use two examples taken from the Skeptic’s Dictionary:

P1: Abortion is the unjustified killing of a human being and as such is murder.

P2: Murder is illegal.

Conclusion: Abortion should be illegal.

Abortion should be illegal if it is murder. This is a tautology. No one would dispute that. But notice how the first premise assumes that abortion is indeed murder. This must not be assumed, but proven. There is no proof that abortion is the killing of a human being.

Begging the question is not a formal fallacy because the argument is valid, in that it is not illogical and the syllogism is correct. But the argument is not sound because the first premise is dubious.

There is nothing wrong with Premise 2. The conclusion is also valid based on the premises. But the argument is still circular reasoning: it assumes the universe exhibits design, but this must be proven not assumed. The assumption is that design exists, but isn’t that what the argument should be proving?

Argument from incredulity / lack of imagination fallacy

“You’re not telling me that humans are descended from single-celled organisms! I can’t believe that!”

Someone’s inability to imagine a scenario is not an argument against it.

Argument from ignorance

In this fallacy, lack of evidence for a contrary viewpoint is taken as evidence in favour of another viewpoint.(Contrary is not the same as contradictory.)

e.g.: “It’s impossible to prove that God doesn’t exist!” one might say.Well, yes.But what does that prove?It’s impossible to prove that there isn’t a deity called the Flying Spaghetti Monster, but that doesn’t mean that it does exist.

In law, a person is assumed innocent until proven guilty.Even if there is no particular evidence that someone is innocent, that doesn’t make them guilty, e.g.:

“No one can prove that Tobe wasn’t at the scene at the time of the crime.”

This proves nothing. Evidence that Tobe was at the scene implies guilt.Anything else is circumstantial at best.

Argument from popularity

This is where someone argues that something must be true or false simply because of the number of people who believe it. However, the number of people who believe something is irrelevant to its veracity.E.g.:

“Billions of people throughout the world believe that god has touched their lives; therefore there must be a religious explanation.”

The fallacy is even more obvious when we say something like: “at one point, everyone thought the earth was flat.”

Indeed, a petition of 600 scientific signatures attesting that evolution couldn’t account for the complexity of life was replied to with a petition of 7000 scientific signatures that said that it could. Whether the petition had 601 or 6 million signatures is irrelevant. The sheer weight of believers on its own means nothing. What matters is whether the evidence supports evolution, not how many people believe it.

False dichotomy

This is also known at the false dilemma, bifurcation, the either-or fallacy, or the fallacy of the excluded middle. E.g.:

“If you’re not with us, you’re against us.”Or:

“If you’re not opposed to the death penalty, then you think criminals should get away with anything they do!”Or:

“Either all life arose by random chance, or it was specially created by god.”

The fallacy is to provide only two possible scenarios when in reality there may be many.

In the fallacious examples above:

1. It’s possible to be neutral and on neither side.

2. Rejection of the death penalty doesn’t mean at all that one opposes punishment and justice.

3. There are at least two other possibilities: life arose by non-random slight successive modifications, ever increasing in complexity. Or, god created life and allowed evolution to happen.

Ad hominem

This is an often misunderstood expression. It does not mean insulting or slandering the opponent. What it means is arguing against someone’s point of view based on that person, instead of their argument. E.g.:

“Joey Noname is a convicted sex offender, so what he has to say on politics is irrelevant.”Or:

“How how you be opposed to eating meat, aren’t you wearing leather shoes?!”

Hypocrisy is always good to expose, but it doesn’t prove anything. I could provide a perfectly sound argument in favour of vegetarianism, whilst eating a greasy quarter-pounder. You might think me hypocritical, or even a liar, but it wouldn’t necessarily mean my argument was wrong.

In Conclusion

What makes an argument right or wrong is its soundness.And of course, there is no substitute for proof or evidence.

The above are a few examples of fallacies that I frequently encounter when debating with people. There are of course many more.

Apart from the above, another great piece of advice is to know your own position, and know that of your opponents. There is no substitute for knowing what you’re talking about and knowing the counter-arguments, otherwise not only might you simply lose the debate, you’ll probably embarrass yourself.

Being a good arguer is about being logical, knowing fallacies, and having knowledge of the subject. Above all, personal biases and emotion are irrelevant. Our most cherished beliefs might be lies. Being a good debater is about wanting truth, whatever that may be.